Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$190.67	10.619%	$210.9172	$210.92	$210.90	$210.90
Purchase #2	$58.80	11.494%	$65.5585	$65.56	$65.55	$65.60
Purchase #3	$73.81	8.854%	$80.3451	$80.35	$80.35	$80.30
Purchase #4	$98.90	11.153%	$109.9303	$109.93	$109.95	$109.90
Purchase #5	$200.28	6.125%	$212.5472	$212.55	$212.55	$212.50
Purchase #6	$136.70	13.439%	$155.0711	$155.07	$155.05	$155.10
Purchase #7	$52.40	13.216%	$59.3252	$59.33	$59.35	$59.30
7 purchase totals =	$811.56		$893.6946	$893.71	$893.70	$893.60